The present invention relates to plasma processing method and apparatus used for dry etching and plasma CVD etc.
In recent years, to effect processing or the like on a semiconductor element at a high aspect ratio by dry etching technique or effect embedding or the like at a high aspect ratio by plasma CVD technique coping with developing dimensional fineness of semiconductor elements, it has been required to effect plasma processing in higher vacuum.
For instance, in the case of dry etching, when a high density plasma is generated in high vacuum, there is a reduced possibility of collision between ions and ions or other neutral gas particles in an ion sheath formed on a substrate surface, and therefore, directions of the ions are aligned toward the substrate surface. Furthermore, because of a high degree of electrolytic dissociation, there results a high incident particle flux ratio of ions arriving at the substrate to neutral radicals. For the above-mentioned reasons, etching anisotropy is improved by generating a high density plasma in high vacuum, thereby allowing processing to be achieved at a high aspect ratio.
Furthermore, in the case of plasma CVD, when a high density plasma is generated in high vacuum, an effect of embedding and flattening a fine pattern can be obtained by a sputtering effect with ions, thereby allowing embedding to be achieved at a high aspect ratio.
As one of plasma processing apparatuses capable of generating high density plasmas in high vacuum, there is a high frequency induction type plasma processing apparatus which generates plasma inside a vacuum vessel by applying a high frequency voltage to a discharge coil. The plasma processing apparatus of this type generates a high frequency magnetic field inside the vacuum vessel and accelerates electrons by generating an induction field inside the vacuum vessel by the high frequency magnetic field to generate plasma.
A known high frequency induction type plasma processing apparatus, has a planar spiral discharge coil 13 as shown in FIG. 15. The planar spiral discharge coil 13 is fixed on a surface opposite to a substrate 14. In FIG. 15, when an appropriate gas is introduced from an introduction inlet 20 into a vacuum vessel 15 while gas inside the vacuum vessel 15 is discharged from a discharge outlet 21 and a high frequency voltage is applied to the planar spiral discharge coil 13 by a discharge coil connected to high frequency power source 16 with the vacuum vessel 15 kept internally at an appropriate pressure, a plasma is generated inside the vacuum vessel 15 to allow the substrate 14 placed on a lower electrode 17 to be subjected to plasma processing such as etching, deposition, and surface improvement. In this case, as shown in FIG. 15, an ion energy reaching the substrate 14 can be controlled by additionally applying a high frequency voltage to the lower electrode 17 from a lower electrode using high frequency power source 18.
However, with the system shown in FIG. 15 a plasma density in-plane distribution is hardly controlled since the planar spiral discharge coil 13 is fixed on the surface opposite to the substrate 14. This will be described in detail below.
As a principal control parameter with regard to the generation of plasma, there can be enumerated gas type, gas flow rate, pressure, high frequency powers, and high frequency power frequencies. In a case where an identical discharge coil is used, the plasma density in-plane distribution varies when these control parameters are varied. An example of the above is shown in FIGS. 16A and 16B. FIG. 16A shows a measurement result obtained by measuring a plasma density distribution on a line parallel to the substrate by a Langmuir probe in the case where the gas type is argon, the gas flow rate is 30 SCCM, the pressure is 5 mTorr and the high frequency power is 1000 W. Uniformity within a range in diameter of 200 mm was a satisfactory value of .+-.2.3%. However, the plasma density distribution in the case where the pressure is 50 mTorr and the other conditions are same results as shown in FIG. 16B, when the uniformity within the range in diameter of 200 mm was .+-.8.8%.
In the case of dry etching, it is sometimes desired to etch a variety of thin films by means of an identical plasma processing apparatus. In such a case, the control parameters such as the gas type and pressure also differ depending on the thin film that is desired to be etched. In the prior art plasma processing apparatus, a certain thin film can be uniformly etched, however, the etching uniformity cannot always be obtained for other thin films. In regard to plasma CVD, the same issue exists.
Furthermore, in the case of dry etching, are varied the control parameters in the course of processing when processing one substrate. For example, in polysilicon etching, there is a process of etching a natural oxide film formed on a surface of polysilicon, and this is followed by a process of etching the polysilicon. These two processes are performed within an identical plasma processing apparatus. However, they have different control parameters, and normally the gas type is changed. In such a case, there arises the issue that no substrate in-plane uniformity of etching characteristics such as etching rate and etching form cannot be obtained when varied plasma density in-plane distributions are provided in the first process and the second process. Not limited to the polysilicon etching, it has been known to change the control parameters in the course of processing one substrate in many plasma processing cases by dry etching and plasma CVD. However, when such a process is performed by means of the prior art plasma processing apparatus as shown in FIG. 15, the substrate in-plane uniformity of the plasma processing cannot be obtained.